Device and method for automatically preventing misting of the windscreen of a vehicle

ABSTRACT

There is described a device for automatically preventing misting of the windscreen of a vehicle, wherein a number of sensors determine ambient conditions capable of misting the windscreen, and, upon such ambient conditions occurring, an electronic central control unit automatically activates the air-conditioning system of the vehicle to direct a stream of hot air onto the windscreen to raise its temperature and so prevent it from misting.

[0001] The present invention relates to a device and method forautomatically preventing misting of the windscreen of a vehicle.

BACKGROUND OF THE INVENTION

[0002] As is known, of the numerous steps taken to improve drivingsafety, many are aimed at distracting the driver's attention from theroad as little as possible, particularly as regards manual interactionwith on-vehicle systems.

[0003] Nevertheless, numerous sources of distraction still remain,foremost of which is undoubtedly demisting the windscreen.

[0004] Demisting a vehicle windscreen, in fact, not only calls forturning on the air-conditioning system fan by hand, and possibly alsoorienting the air inlet ports manually to direct airflow onto thewindscreen, but is also normally performed when the windscreen isalready misted, so that it takes a fairly long time for full visibilitythrough the windscreen to be restored.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide a device andmethod for automatically preventing misting of a vehicle windscreen.

[0006] According to the present invention, there are provided a deviceand method for automatically preventing misting of a vehicle windscreen,as claimed in claims 1 and 9 respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A preferred, non-limiting embodiment of the present inventionwill be described by way of example with reference to the accompanyingdrawings, in which:

[0008]FIG. 1 shows, schematically, a device for automatically preventingmisting of a vehicle windscreen in accordance with the presentinvention;

[0009]FIG. 2 shows an operational flow chart of the method forautomatically preventing misting of a vehicle windscreen according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Number 1 in FIG. 1 indicates as a whole a device in accordancewith the present invention for automatically preventing misting of thewindscreen 2 of a vehicle 3—in the example shown, a motor vehicle.

[0011] Device 1 substantially comprises an internal-temperature sensor 4supplying information relative to the temperature inside the passengercompartment 5 of vehicle 3; an external-temperature sensor 6 supplyinginformation relative to the temperature outside vehicle 3; a relativehumidity sensor 7 supplying information relative to the relativehumidity inside passenger compartment 5 of vehicle 3; ad an electroniccentral control unit 8 connected to sensors 4, 6, 7.

[0012] More specifically, according to one aspect of the presentinvention, the internal-temperature sensor 4 used is conveniently aradiant mean temperature sensor, which is an optical sensor having afield of view whose angle depends on the optics with which it isequipped (e.g. α=30-60°), and comprising a thermocouple housed in avacuum chamber and supplying information relative to the meantemperature radiating from the objects within its field of view. Byadjusting the optics of the radiant mean temperature sensor, the fieldof view of the sensor can therefore be adapted to the conformation ofpassenger compartment 5 of vehicle 3 in which the sensor is housed.

[0013] The internal-temperature sensor is conveniently located insidepassenger compartment 5 of vehicle 3, facing windscreen 2 of vehicle 3,and preferably on the inner face of roof 8 of vehicle 3, adjacent to thecourtesy light (not shown).

[0014] Relative humidity sensor 7 is also located inside passengercompartment 5 of vehicle 3, facing windscreen 2 of vehicle 3, and alsopreferably on the inner face of roof 8 of vehicle 3, adjacent to thecourtesy light.

[0015] As an external-temperature sensor 6, on the other hand, atemperature sensor already provided on vehicle 3 for other purposes isused, e.g. the air-conditioning system temperature sensor, which isnormally located underneath the internal rearview mirror (not shown) ofvehicle 3, or the engine control system temperature sensor, which isnormally located on the air intake conduit (not shown).

[0016] Electronic central control unit 8 is connected to, and receivesthe electric signals generated by, internal-temperature sensor 4,external-temperature sensor 6, and relative humidity sensor 7, andcontrols the air-conditioning system 9 of vehicle 3—shown schematicallyin FIG. 1 by a fan—as a function of the electric signals to preventmisting of windscreen 2 of vehicle 3, as described below with referenceto the operational flow chart in FIG. 2.

[0017] As shown in FIG. 2, electronic central control unit 8 firstacquires the values of internal temperature Ti, external temperature Te,and relative humidity Ur supplied respectively by internal-temperaturesensor 4, external-temperature sensor 6, and relative humidity sensor 7(block 10).

[0018] Electronic central control unit 8 then determines (block 20) thetemperature Tv of the inner face of windscreen 2 of vehicle 3 as afunction of internal temperature Ti and external temperature Te,according to the following equation:${C_{v}\frac{T_{v}}{\tau}} = {{\alpha_{1} \cdot A_{1} \cdot \left( {T_{1} - T_{v}} \right)} - {\frac{a_{e} \cdot \lambda \cdot \lambda_{pvb}}{{a_{e} \cdot \left\lbrack {{\lambda_{pvb} \cdot \left( {s_{1} + s_{3}} \right)} + {\lambda \cdot s_{2}}} \right\rbrack} + {\lambda \cdot \lambda_{pvb}}} \cdot A_{1} \cdot \left( {T_{v} - T_{e}} \right)}}$

[0019] where:

[0020] C_(v)=windscreen heat capacity [J/K]

[0021] T_(v)=windscreen temperature [° C.]

[0022] A₁=windscreen area [m²]

[0023] T_(i)=passenger compartment temperature [° C.]

[0024] T_(e)=external temperature [° C.]

[0025] α₁=internal convective heat exchange coefficient [W/(m².K)]

[0026] α_(e)=external convective heat exchange coefficient [W/(m².K)]

[0027] s₁=inner glass thickness [m]

[0028] s₂=pvb layer thickness [m]

[0029] s₃=outer glass thickness [m]

[0030] λ=glass thermal conductivity [W(m.K)]

[0031] λ_(pvb)=pvb thermal conductivity [W(m.K)]

[0032] Electronic central control unit 8 then determines the dew pointtemperature Tr inside passenger compartment 5 of vehicle 3—that is, thetemperature of the inner face of windscreen 2, below which vapour insidepassenger compartment 5 of vehicle 3 condenses on and mists windscreen2—as a function of internal temperature Ti and relative humidity URinside passenger compartment 5 (block 30).

[0033] More specifically, dew point temperature Tr is calculated asfollows:

[0034] first of all, the actual partial vapour pressure pw [Pa] attemperature Ti [° C.] and relative humidity UR [%] is calculatedaccording to the equation:

pw=6898.55*10{circumflex over( )}(k0+k1/(Ti*1.8+491.72)+k2/(Ti*1.8+491.72){circumflex over( )}2)*UR/100

[0035]  where k0=6.21147, k1=−2886.373, k2=−337269.46;

[0036] documented tables showing water vapour saturation pressure valuesas a function of temperature are then consulted, and, by interpolatingthe table values, dew point temperature Tr [° C.] is the temperaturecorresponding to the actual partial vapour pressure pw defined above andrepresenting saturation pressure.

[0037] At this point, electronic central control unit 8 compares thetemperature Tv of the inner face of windscreen 2 with the dew pointtemperature Tr (block 40).

[0038] As long as the temperature Tv of the inner face of windscreen 2is higher than dew point temperature Tr (NO output of block 40), thephysical conditions required to produce condensation on, and so beginmisting, the inner face of windscreen 2 do not exist, so operation ofelectronic central control unit 8 starts again from block 10.

[0039] Conversely, when the temperature Tv of the inner face ofwindscreen 2 is below dew point temperature Tr (YES output of block 40),the physical conditions required to produce condensation on, and sobegin misting, the inner face of windscreen 2 exist, so electroniccentral control unit 8 accordingly operates the air-conditioning system9 of vehicle 3 to prevent windscreen 2 from misting (block 50).

[0040] More specifically, intervention of electronic central controlunit 8 to prevent windscreen 2 from misting substantially comprisesactivating the fan of air-conditioning system 9; heating the air intakefrom outside or inside vehicle 3 (normally using the heat radiated bythe vehicle engine); and adjusting the air inlet ports to direct hot aironto the inner face of windscreen 2 to increase its temperature and soprevent it from misting.

[0041] Once this is done, operation of electronic central control unit 8starts again from block 10.

[0042] The advantages of the device according to the present inventionwill be clear from the foregoing description.

[0043] In particular, the device according to the invention provides forpredicting well in advance the physical conditions resulting in theformation of condensation on, and initial misting of, the inner face ofthe vehicle windscreen, and intervenes fully automatically to preventthe windscreen from misting. Tests conducted by the Applicant, in fact,show the algorithm described to be capable of predicting misting of thewindscreen approximately three minutes in advance.

[0044] As such, the driver of the vehicle is not required to operate theair-conditioning system to demist the windscreen, and visibility throughthe windscreen is at no time impaired.

[0045] The device according to the invention also provides forpredicting the physical conditions resulting in the formation ofcondensation on the inner face of the vehicle windscreen using a fairlysmall number of sensors—only two, in fact, seeing as how theexternal-temperature sensor used is one already installed on the vehiclefor other purposes—thus enabling advantages in terms of cost, size, andlocation.

[0046] By actually preventing misting of the windscreen, the deviceaccording to the invention is also more convenient energywise, ascompared with conventional demisting, on account of the hysteresisassociated with the change in state of the vapour.

[0047] Clearly, changes may be made to the device as described andillustrated herein without, however, departing from the scope of thepresent invention as defined in the accompanying claims.

[0048] For example, internal and external temperature may be determinedotherwise than as described, e.g. indirectly from other physicalquantities measured on the vehicle.

[0049] The electronic central control unit may intervene differently toprevent misting of the windscreen, and the temperature of the inner faceof the windscreen may be raised otherwise than as described.

1) A device (1) for preventing misting of the windscreen (2) of avehicle (3), characterized by comprising: sensor means (4, 6, 7) fordetecting ambient conditions capable of misting said windscreen (2); andintervention means (8, 9), which are activated automatically, upon saidambient conditions occurring, to prevent misting of said windscreen (2).2) A device as claimed in claim 1, characterized in that saidintervention means (8, 9) comprise ambient condition altering means (9),which are activated automatically, upon said ambient conditionsoccurring, to alter at least one of said ambient conditions, at least inthe vicinity of said windscreen (2). 3) A device as claimed in claim 1,characterized in that said intervention means (8, 9) are activated whena predetermined relationship exists between the temperature of thewindscreen (Tv) and a dew point temperature (Tr). 4) A device as claimedin claim 3, characterized in that said predetermined relationship isdefined by the temperature of the windscreen (Tv) being below the dewpoint temperature (Tr). 5) A device as claimed in claim 1, characterizedin that said sensor means (4, 6, 7) comprise: internal-temperaturesensor means (4) indicating the temperature (Ti) inside the passengercompartment (5) of said vehicle (3); external-temperature sensor means(6) indicating the temperature (Te) outside said vehicle (3); andhumidity sensor means (7) indicating the humidity (UR) inside thepassenger compartment (5) of said vehicle (3). 6) A device as claimed inclaim 5, characterized in that said intervention means (8, 9) comprisecalculating means (20, 30) for calculating the temperature of thewindscreen (Tv) as a function of the temperature (Ti) inside thepassenger compartment (5) of said vehicle (3), and of the temperature(Te) outside said vehicle (3), and for calculating the dew pointtemperature (Tr) as a function of the temperature (Ti) and humidity (UR)inside the passenger compartment (5) of said vehicle (3). 7) A device asclaimed in claim 6, characterized in that said intervention means (8, 9)also comprise comparing means (40) for comparing the temperature of thewindscreen (Tv) with the dew point temperature (Tr), and for activatingsaid intervention means (8, 9) when the temperature of the windscreen(Tv) is below the dew point temperature (Tr). 8) A device as claimed inclaim 6, characterized in that said intervention means (8, 9) alsocomprise air-conditioning means (9); and control means (50) forcontrolling said air-conditioning means (9) so as to direct a stream ofhot air onto said windscreen (2). 9) A method of preventing misting ofthe windscreen of a vehicle, characterized by comprising the steps of:determining ambient conditions capable of misting said windscreen (2);and automatically activating intervention means (8, 9), upon saidambient conditions occurring, to prevent misting of said windscreen (2).10) A method as claimed in claim 9, characterized in that said step ofautomatically activating intervention means (8, 9) comprises the step ofautomatically activating ambient condition altering means (8, 9) toalter at least one of said ambient conditions, at least in the vicinityof said windscreen (2). 11) A method as claimed in claim 9,characterized by comprising the step of activating said interventionmeans (8, 9) when a predetermined relationship exists between thetemperature of the windscreen (Tv) and a dew point temperature (Tr). 12)A method as claimed in claim 11, characterized in that saidpredetermined relationship is defined by the temperature of thewindscreen (Tv) being below the dew point temperature (Tr). 13) A methodas claimed in claim 9, characterized in that said step of determiningambient conditions capable of misting said windscreen (2) comprises thesteps of: determining the temperature (Ti) inside the passengercompartment (5) of said vehicle (3); determining the temperature (Te)outside said vehicle (3); and determining the humidity (UR) inside thepassenger compartment (5) of said vehicle (3). 14) A method as claimedin claim 13, characterized in that said step of automatically activatingsaid intervention means (8, 9) comprises the steps of: calculating thetemperature of the windscreen (Tv) as a function of the temperature (Ti)inside the passenger compartment (5) of said vehicle (3), and of thetemperature outside said vehicle (3); and calculating the dew pointtemperature (Tr) as a function of the temperature (Ti) and humidity (UR)inside the passenger compartment (5) of said vehicle (3). 15) A methodas claimed in claim 14, characterized in that said step of automaticallyactivating said intervention means (8, 9) also comprises the steps of:comparing the temperature of the windscreen (Tv) with the dew pointtemperature (Tr); and automatically activating said intervention means(8, 9) when the temperature of the windscreen (Tv) is below the dewpoint temperature (Tr). 16) A method as claimed in claim 14,characterized in that said step of automatically activating saidintervention means (8, 9) comprises the step of: controllingair-conditioning means (9) of said vehicle (3) so as to direct a streamof hot air onto said windscreen (2).